A cross sea (also referred to as a squared sea or square waves) is a
sea state of
wind-generated ocean waves that form nonparallel wave systems. Cross seas have a large amount of directional spreading.
This may occur when
water waves from one
weather system continue despite a shift in
wind
Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...
. Waves generated by the new wind run at an angle to the old.
Two weather systems that are far from each other may create a cross sea when the waves from the systems meet at a place far from either weather system. Until the older waves have dissipated, they can present a perilous sea hazard.
This sea state is fairly common and a large percentage of ship accidents have been found to occur in this state. Vessels fare better against large waves when sailing directly perpendicular to oncoming surf. In a cross sea scenario, that becomes impossible as sailing into one set of waves necessitates sailing parallel to the other.
Cross seas present a particular hazard for small boats and swimmers, since they can generate rip currents and waves up to .
A cross swell is generated when the wave systems are longer-period
swells, rather than short-period wind-generated waves.
References
Water waves
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